Switch mechanism for pressure-type electrically heated sterilizer



Feb. 2, i954 w. SPRADLING EIAL 4 SWITCH MECHANISM FOR PRESSURE-TYPE ELECTRICALLY HEATED STERILIZER Filed Feb. 12, 1952 5 Sheets-Sheet l INVEN JOSEPH W. SPRADLING PEARL L. ENGLER BY? w ATTORNEY Feb. 2, 1954 Filed Feb. 12, 1952 W SPRADLING ET AL SWITCH MECHANISM FOR PRESSURE-TYPE ELECTRICALLY HEATED STERILIZER 5 Sheets-Sheet 2 N. 2' LL.

ATTORNEY LING ET AL 6 4 OR PRESSURE-TYPE LIZER 5 Sheets-Sheet 3 ATTORN EY J. W. SPRAD SWITCH MECHANISM F ELECTRICALLY HEATED STERI Feb. 2, 1954 Filed Feb. 12, 1952 Feb. 2, 1954 J. W. SPRADLI NG ETAL 2,668,224 SWITCH MEC A ISM o PRESSURE-TYPE ECTRIC ERILIZE Y HE D ST R Filed Feb. 12, 195

5 Sheets-Sheet 4 JOSEPH w A ime sEAR L L. ENGLTER M #AAM ATTORNEY Feb. 2, 1954 J. w. SPRADLING ET AL 2,668,224 SWITCH MECHANISM FOR PRESSURE-TYPE ELECTRICALLY HEATED STERILIZER Filed Feb. 12, 1952 5 Sheets-Sheet 5 ATTORNEY Patented Feb. 2, 1954 SWITCH MECHANISM FOR PRESSURE-TYPE ELECTRICALLY HEATED STERILIZER Joseph W. Spradling and Pearl L. Engler, Madison, Wis., assignors to Air Incorporated, New York,

of New York Reduction Company, N. Y., a corporation Application February 12, 1952, Serial No. 271,198 6 Claims. (Cl. 219-38) This invention relates to electrically heated surgical sterilizing apparatus and particularly to improved electric control switch mechanisms for sterilizers of the pressure type.

In electrically heated pressure sterilizers for surgical goods, the steam necessary to effect the sterilization of the goods is usually generated in a sub-boiler which is connected by suitable means with the sterilizer autoclave. Electrical heating coils are placed in the sub-boiler where steam is generated and then circulated through the autoclave pressure chamber. In order to produce the required sterilization temperature and maintain such temperature for the prescribed length of time, pressure responsive control means are incorporated in the control circuit of the heating coils through which the heating of the coils is controlled to maintain a predetermined steam pressure. As a precaution against damage to the heating elements it has been customary to provide a circuit cut-out switch which prevents operation of the heating coils when the water in the sub-boiler falls below a predetermined level at which the heating elements will become overheated.

Heretofore these types of electric control means have consisted substantially of separate indepen dent devices remotely located on the sterilizer. This arrangement lacks compactness which would enable efiicient use by the operator and involves a great number of bothersome fixtures and fittings. Such controls moreover usually incorporated relay devices in the circuit for control thereof in response to pressure and temperature conditions in the sterilizer. One of the disadvantages of relay devices resides in the necessity for designing different control circuits for A. C. and D. C. power sources which are not interchangeable. A further objection was found in the fact that control switch devices, of an otherwise suitable nature, were limited to a small selection of operating pressures which restricted the utility of such sterilizer apparatus.

It is therefore an object of the present invention to provide in pressure-type, electricallyheated sterilizers an improved electrical switch control mechanism including manual, pressure regulating, and low water cutout controls housed in a single compact unit. v

It is a further object of the invention to provide such a compact control unit which is interchangeable as a control device for either A. C. or D. C. power supplies.

A still further object of the invention is to provide a single compact electrical control unit for pressure type sterilizers which is of improved are not used and which is of adequate power capacity to be applied to sterilizers of substantially any commercially required installation.

In accordance with the invention, a surgical sterilizing apparatus including a pressurized sterilizing vessel and electric coil heating means,

is provided with an improved compact control switch mechanism, comprising a switch housing having a liquid capsule switch element or elements pivotally mounted therein which are adapted to open and close the electric. circuit of the heating coil means. Manual control means are associated with the switch elements to place the switch in operation and pressure responsive means in the switch housing are operatively connected with the switch elements for opening and closing the heating control circuit in response to fluctuations of pressure in said vessel to maintain a substantially constant sterilizing pressure. Temperature responsive means, in said housing are associated with the switch elements for opening the control circuit independently of the pressure responsive means when the temperature in the vicinity of the heating coil means exceeds a predetermined value. The switch elements are preferably mercury capsule switch elements which are in themselves well known and used in various switch devices. One or more of the switch capsule elements are used depending upon the amount of current that must be supplied to the control circuit and carried by the control switch.

Other objects and advantages of the invention will become apparent by reference to the following description and accompanying drawings in which:

Fig. 1 is a front elevation view of a surgical sterilizing apparatus embodying the invention;

Fig. 2 is a side elevation of the sterilizer shown in Fig. 1;

Fig. 3 is a front view partially in section of the switch device in Fig. 1 0f the drawings;

Fig. 4 is a sectional view taken along the line l-d in Fig. 3 looking in the direction of the arrows;

Fig. 5 is a sectional view taken along the line 5-5 in 4- looking in the direction of the arrows, and

Fig. 6 is a schematic perspective illustration of the control switch linkage and cam mechanism.

Referring now to the drawings, a pressure type sterilizer is shown at I!) in Figs. 1 and 2. The sterilizer consists of an autoclave I2 supported in a frame i4 and a sub-boiler H: from which steam is supplied for sterilizing goods placed in the yessel iii. The vessel has a door closure ll of the usual construction through-which such articles may be inserted. The autoclave is substantially identical in construction to one type commonly used comprising an inner shell l8, defining an inner sterilizing chamber 20, and an outer shell or jacket 22 which creates a closed space 24 around the inner shell 18. The sub-boiler IE is connected with the autoclave by means of coupled pipe connections 25. Steam generated in the sub-boiler is delivered through the pipes 26 to the space 24 between the inner and outer sterilizing vessel shells. A pipe 28 opens through the outer shell 22 and delivers the steam, substantially free of condensate, from the space 24, through a steam control valve 36 and pipes 32 and 34 to the inner sterilizing chamber 20. A drain 86 for the air and condensate is provided in the forward lower region of the inner shell l8 having a pip 38 which connects with a steam exhaust line 4! through an air and condensation ejector 42. The exhausting of the chamber 20 is controlled by an exhaust valve 44, Fig. l which allows steam to be exhausted from pipe 28 through the exhaust pipe 49. Thus steam, from pipe 28, is passed through a horizontally disposed vacuum ejector device the exhausting valve 44, and exhaust line M), Fig. 2. The accompanying condensate is discharged into a drain pipe 48 having the usual air gap waste fitting 56. A negative pressure is produced by the ejector 45 in the pipes 32 and 3 3 which draws a vacuum within the chamber 20. The provision of such a vacuum accelerates the drying of the sterilized goods as is well known in the art. A fixture 52 is mounted at the top of the sterilizer autoclave including a safety relief valve and pressure gauges indicating respectively the pressure of steam in the sterilizing chamber and in the space between the inner autoclave shell and the jacket. A thermometer 54, Fig. 1, in the drain line 38 enables a comparison to be made between the temperature in the drain and the tem eratur of saturated steam at the pressure indicated on the pressure gauge of fixture 52 as a test for complete elimination of air as is well understood in the art.

Water is delivered to the sub-boiler through a water supply line 56 having a shut-off valve 58 which permits the boiler to be filled to a desired level as shown on the level indicator 6!], Fig. 1. An electric resistance heating coil 62, extending substantially along the length of the sub-boiler, Fig. 2, and at the bottom thereof, provides the necessary heat to vaporize the water and supply steam for sterilization in th chamber 20. Although only a single coil 62 has been shown, it will be understood that additional coils may be used for sterilizers of larger capacity. The coil 62 is sealed in a water-tight manner in the front end plate of the sub-boiler and extends therethrough to receive suitable electrical connections in a control switch housing 64. The control switch is fastened to the end of the sub-boiler and is also secured by means of a clamp 86 to a crosspiece of the frame I4. The power for energization of the heating coil or coilsis obtained from an A.-C. or D.-C. electric outlet through a power cord such as seen at 68 in Fig. 1., The electric thereon, will be on.

supply circuit of the heating coil or coils is completed by switch means in the control switch 64 which will be described. hereinafter. A pressure tap line 10 is connected in the pipe 2% leading from the subboiler. The pressure in the line is transmitted to pressure responsive means within the control switch housing which operates the control switch device to regulate the generated steam pressure. A temperatur bulb i2 is disposed within the sub-boiler in close proximity to the heating coil which is responsive to excessive heating of the coil or coils 62 when the water falls below a predetermined safe level to open the control circuit.

The control switch device 64 may b briefly described as comprising in general one or more mercury switches attached to a rack such that the rack and mercury switches may be tilted to make or break an electric circuit or circuits through corresponding heating coil elements. The desirable features and advantages of the switch apparatus are found especially in the combination of means for operating, or tipping, the mercury switches. These are as follows:

First by manually turning a control camshaftwith an attached off-on cam. The camshaft has an operative and an inoperative position. In the inoperative position of the cam shaft, the attached off-on cam is positioned against a portion of the mercury switch rack assembly causing the mercury switch rack to tilt such that the mercury switch or switches will be off and will remain off regardless of the operation of other component parts of the device. In this position th heating coil 62 may not be energized. In the operative position of the cam shaft, the attached off-on cam is positioned so that it will not engage the mercury switch rack. With the cam shaft in this position the mercury switch rack will assume a position, partly as an effect of a gravity bias acting on the mercury switch rack and partly because of the effect of a leaf compression spring, such that the mercury switches, independent of other forces acting In this position the heating coil 62 may be energized.

A second means of tipping the mercury switch rack is as follows. With the aforementioned cam' shaft and off-on cam so positioned that the offon cam does not engage the mercury switch rack, operative position, the mercury switch rack may be made to tilt t0 the off position or the on position as a result of an increase or decrease in the pressure within a spring loaded bellows made responsive to the steam pressure in the sterilizer chamber. The movement of the bellows is so compounded through a system of levers that tilting of the mercury switch rack is easily effected by the bellows action.

A third means of tipping the mercury switch rack becomes evident from the following explanation. A latching device is provided in conjunction with the cam shaft. It consists of a spring loaded cutout lever system with a stop pin that may engage a cutout cam, which is attached to the cam shaft, in either the operative or inoperative positions of the cam shaft. This lever system is actuated by a diaphragm capsule as a result of an excessive temperature rise in the vicinity of the cutout bulb 12 mounted adjacent to the heating coil 62 and connected by a tube to the diaphragm capsule. This latching device provides a means of locking the cam shaft in the operative position so the mercury switch rack may be tilted to the on or off positions. F01- 5, low us-anex es ve tem e atu e s in he vicinity. o the to t bulb. the diaph ap expands and actuates the cutout lever system, positioning the lever system so that the cutout cam is disengaged from the latching device in the operative position of the cam shaft and cannot be engaged in the operative position. Therefore, under the action of a torsion spring, the cam shaft will seek the inoperative position and the mercury switch rack will be tilted to the off position. Hence, this mechanism provides another means of tilting the switch rack to the ofi position.

The mercury switches 13, Figs. 4 and 5, are of a well-known design and consist of a glass con-- tainer l4 partly filled with mercury '16 and havingtwo electrodes and all in each mercury switch. Each mercury switch is rigidly attached to a switch rack 82 by spring clips 84. Electrical connections are made to each mercury switch by connecting the electrodeslS and as with insulated wire 86 and 81 respectively as illustrated in Figs. 3 and 5. The insulated wires 85 and 81 attach to terminal blocks 88 and 80 to which suitable electrical connections may be made from the external electrical circuit, through the cord 68, Fig. 1. A pilot light assembly 92 may be provided to indicate the operation of the mercury switches.

It will be noted that the electrical connections for only one of the mercury switches are shown.

Referring to Fig. 3, a conductor 84 connected on terminal block 88 is attached to a terminal connection 86 which is one end of the resistance heating coil 62. The other end terminal c8 of the coil receives a conductor I06 which is connected with a terminal box 102 fastened on the side of a frame I04 of the switch housing. A removable cover Hit, a portion of which is shown in Fig. 3, conceals the inner switch frame Hit. The ter-' minal block 98 is connected with the terminal box by a conductor I00 completing the circuit con-. nections for the single mercury switch and the heating coil 62. Thus when the mercury switch whose connections are shown is placed in on position the electric circuit is completed through the coil t2. It will be seen that the terminal ends of second and third heating coil elements appear in Fig. 3 shown at its and Iii]. Thus the second and third mercury switches 73 may be connected respectively with the corresponding heating coil elements as described for the first mercury switch to provide additional heating capacity. It is preferable that each of the mercury switches and corresponding heating coil units be connected in parallel with each other to divide the total current load and thus reduce the current passed through any single mercury switch. By providing a suitable number of such electrically parallel connected mercury switches a con trol switch of any required capacity may be pro.- vided without exceeding the capacity of a single one of the mercury switches.

Figs. 4, 5, and 6 show the manner in which depending side arms 83 of switch rack .82 are mounted on pivot pins H2 and H3, which are rigidly attached to a switch carriage I {4 and provide a center of rotation for the switch rack 82.

ivot pins H8 and HS are rigidly attached to the-switch carriage tit and may rotate within bearing holes not shown in the frame I04. Stop pins i251 and 22 are rigidly attached to the switch carriage H4. Nctches E23 and I23 are provided in theswitch rack 32 to provide limit stops for the stop pins I20 and $22.

An operating shaft 124,.shown in Figs. 4 5. and 6, is supported at each end of the frame I04 through suitable i bearing holes the frame. A

cutout cam,l2i-1andanofi-on cam in are rigidly attached: to the shaft'I24. These cams I26 and I 28 aramounted in parallel planes perpendiculart to the axis orthe cam-shaft I2 4. A torsion spring 130,-F-igs. t end 6, is wound about the shaft -'I24 "with one endbeing securely fastened to" the cam sh'aft'a-ndthe other end to the frame I04 as shown-at I32, Fig. 6. The bias offered by the torsion spring I=30causesthe shaft to seek and position-itself in: the inoperative position unless held in the operative position by the cutout ca-m I26, aswill become. evident when the cutout lever system is explained.

"Acutout lever l-34, which may be turnedabout a cutout pivot pin I36 that is rigidly attached toa portionofthe frame I04, has a cutout stop pin I38 rigidly attached'thereto. The cutout stop pin I38may-engage the cutout cam I26 in the-operative position of th control shaft I24 as illustrated in Figs. 4, 5, and '6, if the cutout lever I34 is properly positioned, and it may engagethe' cutoutcam in the inoperative" position of the shaft regardless of the position of the cutout leverwithin the limits of its normal movements. The stop I49 and the catch I42 of the cutout cam I26,which are engaged by the stop pin I38 in the inoperative and operative positions-respeetively of the operating shaft I24, are indicated'clearly in Fig.6.

A- rack'finger I44 is securely fastened to the switch rack 82 and may be engaged by the off-on cam I28-when-thecam operating shaft I24 is turned'tothe inoperative position in which the switchzcont-rol-is turned off.

One end of a compression spring I46 rests against abent portion I52 of the frame I04 and the other end'exerts a force against the cutout lever I34 such that it tends to revolve the cutout lever-and cutout stop pin I38 into a position so that the cutout stop pin can engage the cutout cam I26.

A cutout plunger I48, which is constructed so thataportion of it passes through a hole I50 i the cutoutlever I34 and through guides I52 constituting bent portions of frame I04, has a part of its cross section of a greater diameter than-the hole I50 so that the cutout plunger I48 seats against the cutout lever I34 adjacent to the hole 5 As shownimliigs. 4 and 5, a thermal sensitive low water cutoutof a well-known design is rovided as acomponentpart of switch mechanism. Thelow Water cutout consists-principally of a diaphragm capsule I54 which is connected by atube I56-to;the'thermally-responsive bulb I2 mounted in the sub boiler as seen in Fi 2. The bulb I2 is filled witha liquid that vaporize when heated. A diaphragm stud I58 is rigidly fastened to one face of thediaphragm capsule and a threaded Stud I60 is fastened to the opposite face ofgtheqidiaphragm capsule. A nut I62 that fits the thrcadsor the stud I50 fastens the low water cutout assembly to a bracket I63-secured on frame I04. The diaphragm stud I58 may engage the cutout plunger I48 when the diaphragm capsur I54 expands. The force thatv the diaphragm capsuleand the diaphragm stud I58 may exert a ainst the cufmutv p un er I48 is ent o overcome the force of OIQDQSitiOn offered by the compression spring. I46. Hence, an excess of heat inthe vicinityof' the cutout bulb 12 will result in the. cutout lever. I34 being rotated about the .cutc tpi otr n I 6 aga nst the. force o ered. y

the compression spring I46 and the cutout stop aeeaza A bellows I64 is hermetically sealed to a bel lows head I66 which in turn is rigidly fastened to the frame I04. A tapped opening I68 in Fig. 5, in the bellows head I66, allows the tap line 10, Fig. 1, to be attached thereto for the purpose of communicating a change in pressure in pipe 26 to the bellows I64. An actuating head I18 seats against the bellows as shown in a cutaway section of Fig. 4. One end of a compression spring I12 seats against the collar I13 of the actuating head I16 and the other end seats against a yoke I14, as a cutaway section of Fig. 4 illustrates. The yoke I14 has lugs I15 which are in threaded engagement with a pair-of adjusting screws I16 and I18 as shown in a cutaway section of Fig. 5. The adjusting screws I16and I18 are mounted through a bearing in a plate I86 -on the frame I64 and are rigidly attached to gears I82 and I84 respectively, as seen in Fig. 4.

Another gear I86 is rigidly attached to the adjusting screw I18 and gear I84, Fig. 4. The pur-- pose of the gear I86 is to turn a gear train to a pointer I81 of dial I88, Fig. l, to give an indication of the position of the yoke I14. The position of the yoke I14 with respect to the adjusting screws 16 and I16 determines the amountthat the compression spring is compressed and predetermines the amount of pressure within the bellows I64 that will cause the actuating head I'IEI to overcome the force offered by the compression spring I12 and to compress the compression spring, allowing movement of the bellows head.

A gear I88 engages the gears I82 and I84 and. is rigidly attached to a shaft I96, which is free to turn in a bushing I92 fitted in the frame I64. Turning the shaft I68 causes the adjusting screws I16 and I18 to rotate at the same rate and in the same direction with respect to the frame I64. Therefore, the yoke I14 will experience uniform advancement on the adjusting screws.

A pair of side lever arms I94 and I96 are rigidly attached to a crosspiece I98 to form a single rigid link 298. rigidly attached to the frame I04 and fit into bearing holes in the crosspiece I98. The side lever arms I94 and I96 and the crosspiece I 98 are turned as a unit about the pivot pins 282 and 264 by the force of two pivot pins 266 and 298, which are securely attached to the actuatin head I16, acting in slots 2!!! and 2 I2 in the side lever arms I94 and I96. The motion of th side lever arms is transferred to the switch carriage II4 by two switch pins 2M and 2I6 which fit into slots 2I8 and 228 in the side lever arms I94 and I96. This construction is readily seen by referring to Fig. 4 and Fig. 6.

Two stop pins 222 and 224, which are rigidly attached to the switch carriage II4, allow the switch carriage to rotate about the pivot pins H6 and I I8 within the limits established by the con-. tact of the stop pins with the outline of the two limit holes 226 and 228 in the frame I 04.

One end of a leaf compression spring 239 fits into a notch 232 in an ear 234, which is rigidly attached to the frame I64, and the other end fits into a notch 238 in the stop pin 224. The leaf compression spring 236 assures positive action of the mercury switches when the pressure in the bellows I64 is sufficient to overcome the compressive force of the compression spring I12. The leaf compression spring causes a biasing force against the stop pin 224 such that it will tend to tilt the switch carriage H4 and aid the force Two pivot pins 262 and 264 are r 8 exertedby the side lever arms I94 and I96 on the switch carriage H4 and to act either with or against the gravity bias acting on the switch carriage depending upon which side the center of the stop 224 is on the line of centers through the pivot pin H8 and the stop pin 224.

Our invention in actual operation for controlling the operation of an electrically heated steam sterilizer such as sterilizer It would op erate as follows.

The attendant for the sterilizer would turn on the electric power supply to the sterilizer and adjust the water level in the sterilizer boiler to the proper level. The control device would be put in operation by turning the pressure adjusting knob 238 until the desired operating pressure (and consequently temperature if the steam remained saturated) is indicated on the dial I88. Rotation of knob 268 acts through the gear train I88, I82, I84 and I86, moving the indicator I81 of dial I88 and causing rotation of the threaded shafts I16 and I18, Fig. 4. This adjustment sets the operating pressure of bellows I64. The knob 246, Figs. 1 and 2, is operated to rotate cam shaft I24 to the operative position and the mercury switch, or switches, are thus allowed to tilt to the on position closing the electric circuits to the heater elements.

As the heat from the heater elements is transferred to the water in the boiler, the temperature of the water increases and a vapor pressure develops in the sub-boiler I5 and autoclave I2. When the desired operating pressure within the sterilizer chamber is reached the bellows I64 expand, thereby compressing the compression spring I12 and causing the actuating head I16 to move and this motion to be transmitted through the lever system to the switch carriage II 4; if the pressure continues to increase and exceeds the preset operating pressure, the switch carriage i I4, the switch rack 82, and the mercury switches are tilted to the off positionso that the mercury switches are non-conducting, hence shutting oif the power to the heating elements. As radiation and convection carry the heat away from the boiler and sterilizer, the vapor pressure diminishes within these chambers and within the bellows I64. When the pressure in the bollows decreases below the value that the dial or pointer system had been previously set at plus a slight differential determined by the physical characteristics of the leaf compression spring 236 and by the gravity bias acting on the switch rack 82 and the switch carriage H4, the compression spring would compress the bellows and cause the actuating head I16 to move. This motion would be transmitted through the lever system to the switch carriage H4 causing the switch carriage, the switch rack, and the mercury switches to tilt to the on position. This cycle of operation would continue until the operator manually turned the cam operating shaft to the inoperative position, or the low water cutout operated.

In the event that the water level within the steam sub-boiler would fall to a level such that sufficient water was not present to effectively carry the heat away from the heating elements, the temperature of the heating elements and of the low water cutout bulb 12, mounted adjacent to the elements, would increase abnormally. This would cause a vapor pressure to be transmitted from the cutout bulb, through the connecting tube I56 to the diaphragm capsule I54. The diaphragm capsule would expand so as to cause the diaphragm stud I 58 to engage and actuate the cutout plunger M8, forcing the cutout lever I34 to turn against the force of the compression spring 143. This in turn would result in a repositioning of the cutout stop pin 138 so that the cutout cam i26 could not engage the cutout stop pin in the operative position of the operating shaft I24. Therefore, if the cam shaft I24 were positioned in the operative position it would be released and by the action of the torsion spring I30 would turn to the inoperative position of the control shaft in which energization of the heating elements through the switch mechanism is not possible. Until the temperature in the vicinity of the cutout bulb l2 diminished, the cutout stop pin I33 could not engage the cutout cam to retain the shaft I24 in "operative position and the switches can not be closed.

It will now be seen that a preferred embodiment of an improved sterilizer apparatus and electric switch mechanism therefor, embodying several of the features and advantages of the invention hereinbefore mentioned has now been described. The invention is not limited to the specific embodiments herein illustrated and described, but may be used in other ways without departure from its spirit as defined by the following claims.

We claim:

1. An electrically heated sterilizer comprising a frame mounted pressure vessel having a chamber, a water supply inlet, means including an electric heating coil in said chamber and an electric circuit therefor for generating steam and maintaining steam pressure therein, and a unitary control switch mechanism housed in a switch box supported by said frame, said switch mechanism comprising switch elements operable between on and off positions to complete or break, respectively, said circuit to said electric heating coils, said switch elements being biased toward on position to complete said circuit. manually adjustable means movable to inoperative and operative settings, said manual means being biased toward inoperative setting and adapted in said inoperative setting to dispose said switch elements in off position, temperature responsive detent means including a portion extending from said housing and disposed in the vicinity of said heating coils, said detent means being normally operable to retain said manual means in operative setting and responsive to a predetermined temperature of said heating coils to release said manual means, pressure responsive means, means connecting said chamber with said pressure responsive means. and linkage members operatively connecting said pressure responsive means with said switch elements to produce movement of said elements completing or breaking said heating coil circuit to maintain a desired chamber pressure when said manual means is in operative setting.

2. A sterilizer apparatus substantially as set forth in claim 1 wherein said switch elements are carried by a common supporting rack means adapted to be moved to place said switch elements in on and off" positions and said manual and pressure responsive means are operatively connected with said supporting means.

3. A sterilizer apparatus substantially as set forth in claim 2 wherein said switch elements comprise at least one mercury capsule and said means operatively connecting said pressure responsive means and said supporting means comprise a linkage systemincluding an off-centering mechanism effective on either side of a neutral center position of said linkages to urge said linkages away from said center position to thereby assist the regulating effort of said pressure responsive means.

4. A sterilizer apparatus substantially as set forth in claim 3 wherein said pressure responsive means comprises an expansible bellows, said linkage system includes a carriage pivoted in said housing adapted to be rotated by said bellows, said switch supporting rack being pivotably mounted in said carriage, said carriage having means thereon for causing said rack to be rotated with said carriage, said rack being adapted for rotation to off position by said manual means independently of said carriage, and said offcentering mechanism is supported by said switch housing and acts upon said carriage.

5. A sterilizer apparatus substantially as set forth in claim 4, having a resilient member disposed to act against said bellows and means for adjusting the force exerted thereby against said bellows to thereby set the operating pressure of the sterilizer.

6. A sterilizer apparatus according to claim 1 wherein said pressure vessel includes an autoclave and a sub-boiler connected thereto by pipes, said water inlet being adapted to supply water to said sub-boiler, said heating coil forming a part of said switch box housing extending outwardly therefrom and disposed in the lower region of said sub-boiler, said switch box housing being mounted on said sub-boiler and having gasket sealing means therebetween through which said coils extend into the sub-boiler and said temperature responsive means disposed in the vicinity of said heating coils being responsive to a predetermined temperature occurring in the absence of an adequate water supply level to actuate said detent means and prevent setting said manual means in operative position.

JOSEPH W. SPRADLING. PEARL L. ENGLER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,717,216 Isaac June 11, 1929 1,844,263 Alex Feb. 9, 1932 2,369,932 Allen Feb. 20, 1945 2,549,461 Haller Apr. 17, 1951 

